The present disclosure relates to closed cell foam articles, such as sports balls, and related methods for manufacturing such articles. The closed cell foam article is made by a foam injection molding technique. In particular, articles are formed of a closed cell foam material having a density ranging between about 0.050 sg and about 0.800 sg after curing. Some articles include parts that are assembled to create a substantially solid ball with good resilience and other properties mimicking an inflated ball.
Existing sports balls, such as soccer balls or footballs, are often made of an air-filled inner bladder and an outer covering. Existing solid one-piece foam balls are often made from an open cell foam, such as a polyurethane foam. Open cell foam balls, however, typically have an open cell structure, and do not bounce well, are not durable, and may absorb fluids. Another example of a one-piece ball is a solid rubber ball. The largest solid rubber balls are generally about 3 to 4 inches in diameter, and are very heavy and may be dangerous to play with due to their weight.
For certain applications, a closed cell structure is beneficial, for example because the material does not absorb fluids. Other benefits of a closed cell structure include being dirt repellent and easy to clean. This makes a closed cell foam material, such as ethylene vinyl acetate (EVA) foam, particularly suitable for many different applications.
Closed cell foam products are generally much more durable, tougher and lasting than polyurethane or rubber products. Conventionally, EVA foam products are prepared by completely filling a preheated mold with an EVA foamable composition. The foamable composition usually contains EVA resin, a foaming agent, and a cross-linking agent. Pressure is applied to the composition allowing foaming and curing of the composition to take place, i.e., decomposition of the foaming agent and the cross-linking agent, and subsequently releasing pressure to allow the EVA composition to simultaneously expand and cure.
However, the manufacturing of closed cell foam applications with the existing injection molding techniques presents problems, for example curing problems put limitations on the size and shape of the articles formed with the existing methods.
An example of a non-pressurized sports ball is described in U.S. Pat. No. 8,915,810, which is incorporated herein by reference in its entirety. The sports ball is a hollow ball made of an injection molded closed cell elastomeric resin foam. The described process has disadvantages because formation of the sports ball requires that a cap is bonded on. For some applications, such as a pet ball, the construction will not be as durable because the cap can be chewed on and come off. In a massage ball application, the non-pressurized ball cannot take the weight of a body and may deflate so that the ball can no longer function of as a massage ball.
Existing solid round EVA balls that are made by foam injection molding typically have a diameter of less than 2 inches. Because of the foam injection molding process, larger sized applications have manufacturing problems associated because the materials do not cure or harden when a wall thickness of the article is over 2 inches.
Thus, there exists a need for improved closed cell foam articles and manufacturing methods. It is desirable therefore to provide an article that can be larger than the existing closed cell foam articles, that is lightweight, and that is waterproof and more durable than existing articles of similar shape and size. Examples of manufacturing methods to make a lightweight article with the injection molded closed cell elastomeric resin foam technique are disclosed below.